Effective bandwidth approach for the spectral splitting of solar spectrum using diffractive optical elements.

Spectral splitting of the sunlight using diffractive optical elements (DOEs) is an effective method to increase the efficiency of solar panels. Here, we design phase-only DOEs by using an iterative optimization algorithm to spectrally split and simultaneously concentrate solar spectrum. In our calculations, we take material dispersion into account as well as the normalized blackbody spectrum of the sunlight. The algorithm consists of the local search optimization and is strengthened with an outperforming logic operation called MEAN optimization. Using the MEAN optimization algorithm, we demonstrate spectral splitting of a dichromatic light source at 700 nm and 1100 nm with spectral splitting efficiencies of 92% and 94%, respectively. In this manuscript, we introduce an effective bandwidth approach, which reduces the computational time of DOEs from 89 days to 8 days, while preserving the spectral splitting efficiency. Using our effective bandwidth method, we manage to spectrally split light into two separate bands between 400 nm - 700 nm and 701 nm - 1100 nm, with splitting efficiencies of 56% and 63%, respectively. Our outperforming and effective bandwidth design approach can be applied to DOE designs in color holography, spectroscopy, and imaging applications.